1. Field of the Invention
This invention relates to copiers/printers, and more particularly, to an improved method and apparatus for relieving the nip pressure exerted by a weighted ball-on-belt transport in copiers/printers.
2. Description of the Prior Art
In the paper paths of copier/printer machines, it is sometimes necessary to open a nip to relieve the normal force of an idler roll. A necessity could arise, for example, when a downstream nip has control of a sheet and it is desirable to not have the sheet drag in an upstream nip.
Typically, idler rolls are raised using a solenoid, linkage, springs, and the idler roll itself. A special case exists when the upstream transport is a ball-on-belt transport. For example, in a ball-on-belt registration system, a sheet enters the registration area and the transport corrects the skew and the lateral position of the sheet, and transports it forward until the lead edge of the sheet is in a take-away roll. Initially, as soon as the sheet is free from the control of the input nip, the sheet comes under the influence of a cross roll ball/belt nip(s) and its movement is controlled entirely by the forces acting on the sheet: gravity; frictional forces; drag forces from the baffle; the drive force from the ball/belt nip(s); and if the sheet is in contact with the registration edge or front gate, the contact force from the guide or gate. If the sheet had a given skew and also a given lateral offset, the ball/belt(s) will drive the sheet forward, as well as, sidewise, to position the sheet. Removal of the sheet from the system in the event of a sheet jam may cause unwanted drag on the sheet due to the friction on the ball from the spring that acts on the ball radius. The moment created opposes the ball rotation by the sheet. This drag opposes advancement of the sheet by the belt behind it.
Thus, there is still a clear need for an improved ball-on-belt transport system that eliminates the sheet drag problem when a sheet is removed from the system.
Various prior art structures are known for allowing sheets to be removed from a belt transport including the structure shown in the Xerox Disclosure Journal, Vol. 8, Number 1, January/February, Page 25, 1983, that is directed to a paper transport and jam clearance device that includes a transport with a plurality of spaced endless belts entrained around a pair of opposed spaced rollers. Each belt had a metal strip positioned adjacent thereto. Also, in the Xerox Disclosure Journal, Vol. 9, Number 1, January/February 13, pages 13 and 14, 1984 a vertical transport device is shown that controls skewing and mistiming of sheets in a copier/printer paper path by use of magnetic skis.